This invention is related to a method of making a modified silica filler in which silica is contacted with a blend or mixture of (i) an alkyl and aryl group containing dichlorosilane and (ii) a trialkoxysilane free of hydrocarbon or organofunctional groups reactive with a silica surface, in a weight ratio of 1:0.1 to 1:2, respectively. In an alternate embodiment, modified silica fillers can be made by contacting silica with only the alkyl and aryl group containing dichlorosilane.
This is an improvement in methods of modifying silica fillers, as described in for example, U.S. Pat. No. 6,384,125 (May 7, 2002), which is assigned to the same assignee as the present invention. While the ""125 patent refers generally to the use of some similar organometallic compounds and mixtures thereof as the present invention, and their use as hydrophobing agents for silica, it does not describe any particular mixture or blend of organosilicon compounds as being any more effective than any other blend, nor does the ""125 patent identify the existence of any particular ratio of organosilicon compounds as being necessary to achieve a new and unexpected results, i.e., an ability to deposit more siloxane on silica, vis a viz, improved hydrophobicity. In addition, the ""125 patent fails to teach using only single organosilicon compounds of the type of alkyl and aryl group containing dichlorosilanes, as the ""125 patent requires as a second component, what it refers to as a functionalizing coupling agent.
The invention is directed to a method of making modified silica fillers in which silica is contacted with a blend or mixture of organosilicon compounds. In particular, it is directed to an improvement in treating silica with blends or mixtures of (i) an alkyl and aryl group containing dichlorosilane and (ii) a trialkoxysilane free of hydrocarbon or organofunctional groups reactive with a silica surface, in weight ratios of 1:0.1 to 1:2, respectively. Preferably, the weight ratio is 1:0.3 to 1:1, and most preferably the weight ratio is 1:0.5. In another embodiment, the treating agent for silica may consist of only (i) the alkyl and aryl group containing dichlorosilane.
In particular, the invention is directed to a method of making modified silica fillers in which silica surfaces are contacted with compositions containing organosilicon compounds. The improvement consists of treating silica surfaces with compositions in which the organosilicon compounds in the compositions are only of types of structural groups of monomeric dichlorosilanes and trialkoxysilanes. The compositions may be (i) mixtures or blends of alkyl and aryl group containing dichlorosilanes and trialkoxysilanes free of hydrocarbon or organofunctional groups reactive with silica surfaces, (ii) mixtures or blends of substituted alkyl and substituted aryl group containing dichlorosilanes in which the dichlorosilanes are free of hydrocarbon or organofunctional groups reactive with silica surfaces and trialkoxysilanes free of hydrocarbon or organofunctional groups reactive with silica surfaces, or (iii) substituted and unsubstituted alkyl and aryl group containing dichlorosilanes in which the dichlorosilanes are free of hydrocarbon or organofunctional groups reactive with silica surfaces. The mixtures and blends contain dichlorosilanes and trialkoxysilanes in a weight ratio of 1:0.1 to 1:2, respectively.
These and other features of the invention will become apparent from a consideration of the detailed description.
The silica used to make the modified silica fillers according to this invention are the colloidal or precipitated silicas of the type used to formulate polymeric compositions such as rubber, particularly those rubber compositions used in the manufacture of vehicle tires for improving the mechanical properties of tire rubber. Such silicas are described in much detail in the ""125 patent to which reference may be had, and which is considered as being incorporated herein by reference thereto.
Mineral fillers such as silica, having a small particle size and a large surface area, are capable of increasing the tensile strength of rubber compounds and therefore are useful as reinforcing materials for rubber; particularly when the mineral surfaces of the filler are converted to hydrophobic low energy surfaces.
Silica treating agents according to the invention are mixtures and blends of alkyl and aryl group containing dichlorosilanes, and trialkoxysilanes, both of which are preferably free of hydrocarbon or organofunctional groups reactive with silica surfaces. Thus, the organosilicon compounds useful according to the invention may contain alkyl groups, cycloalkyl groups, araalkyl (arylalkyl) groups, allaryl (alkylaryl) groups, aryl groups, and certain substituted groups which are not reactive with respect to silica surfaces.
Some examples of alkyl groups are methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, octadecyl, and nonadecyl. Some examples of cycloalkyl groups are cyclobutyl and cyclohexyl. Some examples of araalkyl (arylalkyl) groups are benzyl, phenylethyl, and 2-phenylpropyl. Some examples of alkaryl (alkylaryl) groups are tolyl and mesityl. Some examples of aryl groups are phenyl, xenyl, naphthyl, and anthracyl. Some examples of substituted groups which are not reactive with respect to silica surfaces are halogenated alkyl groups and aryl groups such as chloromethyl, dichloromethyl, trichloromethyl, 3-chloropropyl, chlorocyclohexyl, chlorophenyl, and dichloroxenyl; alkyl groups containing alkoxy radicals such as methoxy, ethoxy, butoxy, and pentoxy; alkyl groups containing sulfido (xe2x80x94Sxe2x80x94), disulfido, or polysulfido radicals; and alkyl groups containing cyano (xe2x80x94Cxe2x89xa1N) radicals.
Representative of some suitable alkyl and aryl group containing dichlorosilanes are t-butylphenyldichlorosilane, chlorophenylmethyldichlorosilane, phenylethyldichlorosilane, phenylmethyldichlorosilane (methylphenyldichlorosilane) (MPDCS), and p-tolylmethyldichlorosilane.
Representative of some suitable trialkoxysilanes are benzyltriethoxysilane, 2-chloroethyltriethoxysilane, (p-chloromethyl)phenyltrimethoxysilane, (p-chloromethyl)phenyltri-n-propoxysilane, chloromethyltriethoxysilane, chloromethyltrimethoxysilane, chlorophenyltrietioxysilane, 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 2-cyanoethyltriethoxysilane, 2-cyanoethyltrimethoxysilane, 3-cyanopropyltriethoxysilane, 3-cyanopropyltrimethoxysilane, 11-cyanoundecyltrimethoxysilane, cyclohexyltrimethoxysilane, ethyltriethoxysilane, ethyltrimethoxysilane, 3-mercaptopropyltriethoxysilane (MPTES), 3-mercaptopropyltrimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, pentyltriethoxysilane, phenethyltrimethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, n-propyltriethoxysilane, n-propyltrimethoxysilane, and p-tolyltrimethoxysilane.
A general method of making modified silica fillers according to the invention is described below in Example A, although the modified silica fillers can be made by any known and accepted technique, for example, as described in detail in the ""125 patent, in U.S. Pat. No. 5,908,660 (Jun. 1, 1999), and in U.S. Pat. No. 6,051,672 (Apr. 18, 2000). While these patents describe general methods, they fail to describe the features of this invention, i.e., the use of a particular mixture or blend of organosilicon compound(s) in a particular ratio.
When used in rubber compositions for manufacturing vehicle tires, other conventional additives may be used along with the modified silica filler, including other fillers such as carbon black, various oils, plasticizers, accelerators, antioxidants, heat stabilizers, light stabilizers, zone stabilizers, extenders, and coloring pigments.